... which would require error handling on all of the call stack upwards,
which is not that trivial an endavour. Also, for the calls via
VSMW_DestroyCluster(), we are actually about to free space, but
temporarily need more.

Other ideas:

- panic, but leave a better error message
- monitor free space and refuse loading vcls if insufficient
- maybe as part of some more general vcl management (e.g.
  "maintain max xx vcls loaded - aka auto-discard)

Ref #2764